I used a diamond chip drum in a moto tool.......I didnt worry too much since the pins only function is to prevent the ring from rotating and fine machining didnt seem necessary ....fits and runs OK post surgery and the CR is definitley higher.......Apparentley any newer 31 cc now has two rings with a better seal and compression as a result as it comes from the factory,and I dont know if the Bowman ring fits or not,although Im sure he will make them for anyone that wants to buy two and try.